Old Hard Drives

Well this is repeat of yesterdays post but what do you do with old hard drives?  This seems like a recurring theme the last couple days because it seems stupid to put a 40 GB drive in my computer when I have two 120 GB drives.  I also don’t want to throw these out because I had personal data on them that I wouldn’t want other people finding.  My guess is that people will look at if they purchased it from my off eBay.  I guess I will have to start looking at ways to delete whole hard drives.